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LDL Cholesterol — Friedewald Calculator

Estimate LDL cholesterol from total cholesterol, HDL and triglycerides using the Friedewald formula — with ATP III risk bands.

Units

ATP III risk bands (NCEP)

Optimal
< 100 mg/dL
Near optimal
100 – 129 mg/dL
Borderline high
130 – 159 mg/dL
High
160 – 189 mg/dL
Very high
≥ 190 mg/dL

Formula

LDL = Total − HDL − Triglycerides / 5 (mg/dL)

The Friedewald formula (1972) estimates LDL from total cholesterol, HDL and triglycerides. It is the most widely used method in routine lipid panels — as long as triglycerides remain below 400 mg/dL (4.5 mmol/L).

Frequently Asked Questions

What is the Friedewald formula?+
Introduced by William T. Friedewald in 1972, this formula estimates LDL cholesterol from total cholesterol, HDL and triglycerides — without needing a direct LDL assay. The estimate is robust when triglycerides are below 400 mg/dL (4.5 mmol/L).
When is the estimate unreliable?+
Once triglycerides reach 400 mg/dL (4.5 mmol/L) Friedewald systematically underestimates LDL. In that case request a direct LDL measurement, or use the Sampson or Martin-Hopkins equations.
What LDL values are considered optimal?+
Per NCEP ATP III, LDL below 100 mg/dL is optimal, 100–129 near optimal, 130–159 borderline high, 160–189 high, and 190 or above very high.
Do I need to fast?+
Yes — triglycerides are strongly affected by recent meals. For a valid Friedewald estimate, fast for 9–12 hours before the blood draw.
What can I do about high LDL?+
Lifestyle measures come first: a fibre-rich diet, fewer saturated and trans fats, regular exercise, and weight loss when needed. For LDL ≥ 190 mg/dL — or additional risk factors — pharmacotherapy (statins) may be indicated.
Why are ATP III bands defined in mg/dL?+
The NCEP ATP III guideline comes from the US, where cholesterol is reported in mg/dL. Other regions use mmol/L — the calculator converts automatically for band classification (factor 38.67).

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Background

LDL Cholesterol (Friedewald) Calculator Guide: Formula, Limits, Values

8 min